It is common practice during surgical procedures in which the patient is subjected to a general anesthetic to monitor various body functions using a flexible catheter inserted through the patients' nose into the esophagus. For example, U.S. Pat. Nos. 4,476,872, 4,439,031, 4,176,660 and 3,951,136 disclose an esophageal catheter used for monitoring the patient's electrocardiogram, heartbeat and temperature. Similarly, U.S. Pat. Nos. 4,763,663 and 4,619,268 disclose esophageal catheters which monitor heart sounds and body temperature. U.S. Pat. No. 4,475,555 discloses an esophageal probe with a universal measuring attachment to which may be adapted a stethoscope for measuring body sounds, a temperature sensor for measuring body temperature, pressure transducers or light sources.
Two prior art esophageal catheters include electrodes which may be used for diagnostic pacing. One such device is the Azbacher Pill Electrode for diagnostic pacing; the second is the Seecor Model Stat Pace II transvenous wire which may be fed into the esophagus. In these devices the patient's heart is temporarily paced to a high rate, such as 120 beats per minute, the pacing signal is removed and the patient's heart is then monitored with the ECG sensor to determine the rate and function to which it returns after removal of the diagnostic pacing pulses. The pacing electrodes in these catheters, however, have a relatively small surface area and thus generate a high current density which would burn the patient's esophagus if pacing continued beyond a short period of time.
A problem present in every surgical procedure in which the patient is administered a general anesthesia is the possibility that the patient's heart will beat erratically or too slowly or cease functioning completely in response to the anesthesia or stresses of surgery. In such cases the anesthesiologist and other members of the surgical team must act quickly to restore the patient's heart to its normal rhythm. This is typically done by applying an external pacer to the patient. Doing so, however, requires that at least one external electrode be applied to the patient's chest. In some surgical procedures it is difficult, if not impossible, to employ these emergency procedures. For example, if the patient is undergoing back surgery, he may be positioned face down on the operating table and incapable of movement without severe injury, so that application of the pacing electrodes may be extremely hazardous to the patient.